Mechanistic studies of the electrochemical polymerization of C60 in the presence of dioxygen or C60O

Abstract

Electropolymerization of C₆₀ in the presence of dioxygen, in a mixture of acetonitrile and toluene (1 : 4, v : v) containing tetra(alkyl)ammonium perchlorate, was investigated by multi-scan cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. The fullerene was readily electropolymerized if the O₂ to C₆₀ concentration ratio in solution exceeded 1 : 10 and the applied potential reached values where electro-reduction of dioxygen to superoxide, O₂˙⁻, and C₆₀ to C₆₀²⁻ occurred. The redox activity of the polymer was determined by cyclic voltammetry for solutions with different tetra-(alkyl)ammonium perchlorates used as supporting electrolytes. The film conductivity was higher the smaller the size of the cation in the supporting electrolyte. The C₆₀ electropolymerization in the presence of dioxygen was suppressed when a spin trapping agent, N-tert-butyl-α-(4-nitrophenyl)nitrone that could intercept superoxide, was present. The fullerene was also electropolymerized in the presence of small amounts of the epoxide, C₆₀O, in the absence of dioxygen. We postulate that the C₆₀ electropolymerization in the presence of O₂ proceeds via the initial nucleophilic attack of superoxide on C₆₀ to form a C₆₀O₂˙⁻ radical anion, which then interacts with another molecule of C₆₀ to produce C₆₀O and C₆₀O˙⁻. Under further electro-reduction, these intermediates serve to initiate polymerization of C₆₀ through the formation of C₆₀O²⁻, as determined earlier in studies of the electropolymerization of C₆₀O itself.